Proportional pressure control valves which are provided with load sensing feedback control are well known. In such valves, the degree of communication between an inlet port and an outlet port is in part determined by an electrical signal applied to an electromagnetic coil for operating the valve and also by the pressure at the outlet port. Typically, a higher pressure at the outlet port tends to close off the passageway between the inlet port and the outlet port.
This is achieved by the outlet port pressure acting on a certain area of the valve control element, for example a spool, tending to move the element axially so as to choke off the passageway between the inlet port and the outlet port. The magnitude of the force exerted on the valve control element to move it axially is determined in part by the magnitude of the pressure, but also by the net area of the spool on which the pressure acts.
In the prior art, this area has been provided by forming a blind bore in the spool and providing a pressure feedback pin slidable in the open end of the blind bore on which the pressure acted. However, especially for large pressures, the net area on which the pressure acts is very important. In the prior art design, this area was determined by the diameter of the pin, and therefore, small areas, required for high pressures, required a small diameter pin, which also placed a constraint on the diameter of the bore in the valve element in which the pin was slidable, since that is essentially the same as the diameter of the pin in order to minimize leakage.